Method of assembling a friction clutch

ABSTRACT

The axially movable pressure plate of a friction clutch for motor vehicles is non-rotatably secured to the housing by a set of leaf springs each of which has an end portion overlying that surface of the pressure plate which faces away from the clutch plate. The end portion of each leaf spring has an opening in register with the open end of a blind bore in the surface of the pressure plate. Such end portions of the leaf springs are permanently fastened to the pressure plate by tubular connecting elements having (a) enlarged end portions overlying those sides of the leaf springs which face away from the pressure plate and (b) main portions which extend through the respective openings and into the registering blind bores and are radially expanded into pronounced frictional engagement with the pressure plate. The plastically deformable material of the main portions of the connecting elements is expanded by an extractible tool or by discrete spreading pins which are driven into open-ended sockets of the connecting elements and remain therein to maintain the main portions in radially expanded condition. The connecting elements contribute to a reduction of the overall weight of the friction clutch, to a reduction of the dimensions of the clutch, as considered in the axial and radial directions, to a reduction of the weight of the clutch, and to greater reliability of the connections between the leaf springs and the pressure plate and hence to greater safety of the clutch.

This application is a division, of application Ser. No. 509,190, filedJune 29, 1983, now U.S. Pat. No. 4,615,424.

CROSS-REFERENCE TO RELATED CASE

The friction clutch which is disclosed in the present application issimilar to the friction clutch described in my commonly owned copendingpatent application Ser. No. 509,190 filed June 29, 1983 for "Fasteningdevices for friction clutches and method of assembling such fasteningdevices".

BACKGROUND OF THE INVENTION

The present invention relates to friction clutches in general,especially to friction clutches for use in motor vehicles, and moreparticularly to improvements in friction clutches of the type whereincertain components are non-rotatably but axially movably coupled to eachother by leaf springs or other deformable coupling means.

It is well known to construct a friction clutch in such a way that adiaphragm spring or another suitable energy storing device urges apressure plate against the friction lining of a clutch plate or disc andthat the pressure plate is axially movably but non-rotatably secured tothe clutch housing, e.g., to a cover of the housing, by severalequidistant sets of leaf springs which are deformable in directions toallow for axial movements of the pressure plate under or against thebias of the diaphragm spring. Reference may be had, for example, toGerman Offenlegungsschrift No. 1,600,093 which discloses a frictionclutch of the just outlined character. In the clutch of this Germanpublication, the pressure plate is provided with equidistant projections(as considered in the circumferential direction of the clutch) whichextend radially outwardly and each of which is connected with one endportion of a leaf spring by means of a rivet. The other end portions ofthe leaf springs are connected to the housing of the friction clutch.The orientation of the leaf springs is such that they allow the pressureplate to move axially of the housing but the pressure plate and thehousing are held against angular movement with reference to one another.The shanks of the rivets extend through openings which are providedtherefor in the respective end portions of the leaf springs. The shankof each rivet also extends through a hole in the respective projectionof the pressure plate, and the rivets have heads adjacent to those sidesof the projections which fact away from the respective leaf springs. Thespace requirements of the rivet heads at the exterior of the pressureplate contribute to the axial dimensions of the friction clutch.Moreover, the projections (which are provided for the express purpose ofsupporting the respective end portions of the leaf springs) contributeto the dimensions of the friction clutch, as considered in the radialdirection of the clutch housing. This creates problems in many types ofcompact vehicles where the space is at a premium and, moreover, theprojections of the pressure plate contribute to the weight of theclutch. Still further, centrifugal force acting upon the projectionsrenders it necessary to increase the weight, mass and bulk of thecircular main portion of the pressure plate so that such main portioncan stand the developing stresses even if the pressure plate is rotatedat a very high speed. The standards regarding the bursting strength ofpressure plates in friction clutches are very high and must be met bythe component parts of friction clutches which are intended for use inmotor vehicles and the like.

Another mode of securing the end portions of leaf springs to an axiallymovable pressure plate in a friction clutch is disclosed in U.S. Pat.No. 3,283,864 granted Nov. 8, 1966 to Motsch. The fastening meanscomprises rivets extending through those portions of the pressure platewhich bear against the clutch disc when the clutch is to transmittorque. To this end, the pressure plate is formed with an annulus ofthrough holes in the region of its friction generating surface, and eachhole has an enlarged portion at that end which terminates in thefriction surface. The shank of each rivet extends through the opening ofthe respective leaf spring and through the smaller-diameter portion ofthe respective through hole in the pressure plate, and each rivet has ahead in the larger-diameter portion of the respective hole. A drawbackof such proposal is that the making of holes in the annular portion ofthe pressure plate reduces the area of the friction surface (namely, ofthe surface which engages the adjacent lining of the clutch disc whenthe clutch is engaged), especially since the larger-diameter ends ofsuch holes terminate at the friction surface. This means that theremaining portion of the friction surface is subjected to morepronounced wear, especially in the regions between the neighboringholes, and the friction surface is likely to develop pronounced channelsor furrows after a relatively short period of use. The development offurrows in the friction surface adversely influences the torquetransmitting action because it affects the frictional engagement betweensuch surface and the adjacent lining of the clutch disc. Still further,weakening of the pressure plate due to the provision of through holes inthe friction surface entails localized accumulations of heat withattendant development of internal stresses and distortion of thepressure plate. The distortion can be so pronounced that it preventsdisengagement of the pressure plate from the clutch disc and/or delayssuch disengagement and/or allows for mere partial disengagement of suchparts from one another. Moreover, localized accumulations of heat in theregions of through holes are likely to entail the development of crackswhich, in turn, can cause the pressure plate to burst within the higherRPM range.

A further mode of fastening leaf springs to the pressure plate of afriction clutch is disclosed in German Utility Model No. 1,925,053. Thefastening means includes hollow screws which extend into tapped bores ofthe pressure plate. A drawback of such proposal is that vibrations,which are bound to develop when the friction clutch is in use in a motorvehicle or the like, cause the screws to become loose and to thus putnot only the clutch but also the entire vehicle out of commission.Loosening of screws in the pressure plate is believed to be attributableto the absence of accurate mesh between the external threads of thescrews and the internal threads of the pressure plate, i.e., to theabsence of reliable and uniform transmission of forces between thepressure plate and the springs. This results in overstressing andexcessive wear upon certain portions of the windings of the threads withattendant loosening of the screws and a breakdown of the connectionsbetween the leaf springs and the pressure plate. A further drawback ofthe just described fastening means is that the dimensions of openings inthe leaf springs must be selected with utmost accuracy in order toprevent wobbling of the leaf springs with reference to the shanks of thescrews. Any wobbling of the leaf springs would even further increase thelikelihood of rapid loosening of the screws and would also result inpronounced wear upon the material of the leaf springs around therespective openings. This would entail immediate or rapid separation ofleaf springs from the pressure plate.

OBJECTS AND SUMMARY OF THE INVENTION

An object of the invention is to provide a novel and improved connectionbetween certain components of a friction clutch, especially between thehousing and the axially movable pressure plate of a friction clutch foruse in motor vehicles.

Another object of the invention is to provide novel and improved meansfor fastening the end portions of leaf springs or analogous deformablecoupling members to the pressure plate of a friction clutch in such away that the connections are more reliable, longer lasting, simpler andless expensive than the aforediscussed and other conventionalconnections.

A further object of the invention is to provide fastening means of theabove outlined character which contribute little, if anything, to theweight and bulk of the clutch, not only in the radial but also in theaxial direction, and which can stand vibrations and other straymovements of component parts of the clutch more readily than heretoforeknown fastening means.

An additional object of the invention is to provide fastening meanswhich can be assembled and applied with little loss in time and byresort to relatively simple tools.

Still another object of the invention is to provide a novel and improvedmethod of establishing reliable connections between certain constituentsof friction clutches for use in motor vehicles or the like.

An additional object of the invention is to provide a method which canbe practiced with resort to simple machinery and tools, and whichensures the establishment of longer-lasting and more reliableconnections than in accordance with heretofore known proposals.

A further object of the invention is to provide a friction clutch whichembodies one or more fastening means of the above outlined character.

Another object of the invention is to provide a motor vehicle embodyinga clutch which features one or more fastening means of theaforedescribed character.

One feature of the invention resides in the provision of a method offastening a leaf spring to a pressure plate in a friction clutch,particularly in a friction clutch for motor vehicles. The methodcomprises the steps of providing a surface of the pressure plate with ablind bore (such surface preferably faces away from the clutch plateagainst which the pressure plate is movable in order to engage theclutch), providing one end portion of the leaf spring with an openingand placing the opening into register with the open end of the blindbore so that one side of the leaf spring faces away from theaforementioned surface of the pressure plate, introducing into theopening and into the registering blind bore a plastically deformabletube which has an enlarged end portion overlying the aforementioned sideof the spring, and expanding at least a part of the tube in the blindbore radially so as to move the expanded part of the tube intopronounced frictional engagement with the pressure plate.

The expanding step can comprise driving into the tube a tool whosecross-sectional area exceeds, at least in part, the inner diameter ofthe tube. The tool can be left in the interior of the expanded tube, orit can be extracted upon completion of the expanding step.

The method can further comprise the step of expanding an end portion ofthe tube in the region which is outwardly adjacent to the aforementionedside of the leaf spring so that the thus expanded end portion of thetube constitutes the aforementioned enlarged end portion.

Another feature of the invention resides in the provision of a frictionclutch, particularly for motor vehicles, comprising first and secondrotary components which are coaxial with one another and at least thefirst of which is movable axially relative to the second component, anda coupling member including a first portion which is secured to one ofthe two components and a second portion which overlies the othercomponent and has an opening (e.g., a non-circular opening). Thatsurface of the other component which is adjacent to the second portionof the coupling member has a blind bore in register with the opening ofthe second portion, and the clutch further comprises means for fasteningthe second portion of the coupling member to the other component. Suchfastening means includes a connecting element which extends through theopening and has an at least partially expanded first portion received inthe blind bore and being in pronounced frictional engagement with theother component. The connecting element further includes an end portionoverlying (in the region of the opening) that side of the second portionof the coupling member which faces away from the other component andserving to hold the second portion of the coupling member againstmovement away from the adjacent surface of the other component.

The first component can constitute a pressure plate, and the secondcomponent can constitute or form part of the clutch housing. Thecoupling member can comprise a single leaf spring or a package ofoverlapping leaf springs, and the first portion of the connectingelement can constitute a tube. Such clutch further comprises a clutchplate adjacent to that (second) surface of the pressure plate whichfaces away from the second portion of the leaf spring or springs, and aclutch spring (e.g., a diaphragm spring) which reacts against thehousing and bears against the pressure plate so as to urge the latteragainst the clutch plate. The pressure plate can constitute an annulusand its second surface bears against a friction lining of the clutchplate when the clutch spring is free to maintain the pressure plate infrictional engagement with the lining of the clutch plate.

The pressure plate can be provided with a profiled internal surfacewhich surrounds at least a portion of the blind bore, and the externalsurface of the first portion of the connecting element is preferablyheld in intimate contact with the internal surface of the pressureplate. The first portion of the connecting element consists, at least inpart, of a plastically deformable (ductile) material (preferably asuitable metal), and the just mentioned external surface is thenprovided on such plastically deformable material. The internal surfaceof the pressure plate can be threaded. If the external surface of thefirst portion of the connecting element is profiled (in addition to orin lieu of the internal surface of the pressure plate), the profile ofsuch external surface can be formed by one or more threads.

The connecting element can be provided with a socket which is open inthe region of the end portion of the connecting element, and thefastening means can further comprise a spreading element which is driveninto the socket to maintain the first portion of the connecting elementin expanded condition. Such first portion can be integral with the endportion of the connecting element. The socket can comprise a firstportion of greater diameter and a second portion of smaller diameter,and at least the major part of the spreading element can be received inthe first portion of the socket. The spreading element can comprise asubstantially conical (e.g., frustoconical) end portion which isdisposed in the blind bore and is remote from that surface of thepressure plate which is adjacent to the second portion of the leafspring, i.e., the conical portion can be disposed in or close to thedeepmost portion of the socket. The apex angle of the conical orfrustoconical portion of the spreading element is preferably betweenabout 30 and 60 degrees, most preferably about 40 degrees.Alternatively, the spreading element can comprise a substantiallyspherical (preferably hemispherical) end portion which is disposed in orclose to the deepmost portion of the socket. The spreading elementeffects radial expansion of at least a part of the plasticallydeformable first portion of the connecting element to thus ensure thatsuch first portion is in requisite frictional engagement with theinternal surface of the pressure plate. The end portion of theconnecting element can constitute or resemble an annulus which surroundsthe opening of the second portion of the leaf spring at that side of theleaf spring which faces away from the pressure plate. The spreadingelement can completely fill the socket of the connecting element, andits outer end face can be flush with the exposed end face of the annularor otherwise configurated end portion of the connecting element. As arule, the end portion of the connecting element will or can constitute adeformed part of the first portion. The extent or nature of radialexpansion or deformation of the first portion of the connecting elementcan be such that this first portion completely fills the opening of theleaf spring.

If desired, the socket of the connecting element can remain empty. Forexample, the socket can be formed by a suitable spreading tool which isthereupon extracted from the socket so that the deformed or expandedconnecting element resembles a sleeve one end of which is but need notbe closed and the other end of which has a radially outwardly extendingcollar constituting the aforementioned end portion of the connectingelement.

If a spreading element (e.g., a pin) is used to fill the socket of theconnecting element, that (outer) end portion of the spreading elementwhich is surrounded by the end portion of the connecting element ispreferably closely surrounded by the material of the end portion of theconnecting element so as to prevent axial shifting of the spreadingelement. The cross-sectional area of that (major) portion of thespreading element which is received in the inner part of the socket(i.e., which is surrounded by the first portion of the connectingelement in the blind bore of the pressure plate) preferably exceeds thecross-sectional area of the outer end portion. The latter can constituteor resemble a portion of a sphere or a portion of a cone whosecross-sectional area decreases in a direction away from the blind bore.

The novel features which are considered as characteristic of theinvention are set forth in particular in the appended claims. Theimproved fastening means itself, however, both as to its constructionand the mode of assembling the same, together with additional featuresand advantages thereof, will be best understood upon perusal of thefollowing detailed description of certain specific embodiments withreference to the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a fragmentary axial sectional view of a friction clutchwherein an end portion of a package of overlapping leaf springs isfastened to an axially movable pressure plate of the clutch inaccordance with a first embodiment of the invention;

FIG. 2 is a fragmentary plan view of the friction clutch, as seen in thedirection of arrow II in FIG. 1;

FIG. 3 illustrates a detail in the structure of FIG. 1 and shows theinitial stage of driving a spreading element into the socket of aconnecting element forming part of the improved fastening means;

FIG. 4 is an elevational view of a modified spreading element having asubstantially hemispherical end portion; and

FIG. 5 is a view similar to that of FIG. 3 but showing a modifiedfastening means whose tubular connecting element is radially expandibleby a retractible tool.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring first to FIGS. 1 and 2, there is shown a portion of a frictionclutch which comprises an axially movable pressure plate 1, a housing 2including a cover which overlies the pressure plate 1, a diaphragmspring 3 which reacts against and is secured to the housing 2 by anannulus of rivets 3a so that it can flex in the region of two coaxialring-shaped seats 3b, 3c and can bear against axailly extendingprotuberances 1a of the pressure plate 1, and a clutch disc or clutchplate 4 which is in contact with the adjacent friction surface 10 of thepressure plate when the latter is free to follow the bias of thediaphragm spring 3. The rivets 3a further serve to hold the seats 3b, 3cagainst axial and/or radial movement with reference to the diaphragmspring 3 and housing 2. The clutch is engaged when the friction surface10 of the pressure plate 1 is free to bear, with requisite force,against the adjacent surface of the clutch disc 4 which is therebycompelled to bear against a torque transmitting element, e.g., aflywheel (not shown) receiving rotary motion from the crankshaft of aninternal combustion engine.

The means for coupling the pressure plate 1 to the housing 2 in such away that the pressure plate is held against rotation but is movableaxially of the housing (into and from frictional engagement with theclutch disc 4) comprises a set of equidistant leaf springs 5 each havinga first end portion 5a secured to the housing 2 by a rivet 6 and asecond end portion 5b secured to the pressure plate 1 by a fasteningdevice 7 which is constructed, mounted and assembled in accordance withan embodiment of the present invention.

The fastening device 7, which is shown in FIGS. 1, 2 and 3 of thedrawing, comprises a tubular connecting element 12 and a spreading orexpanding element 13. The tubular first portions 12a of the connectingelements 12 extend through the openings 5c which are provided in thesecond portions 5b of the respective leaf springs 5 and into registeringblind bores 11 which are machined into or otherwise formed in thatsurface (10a) of the pressure plate 1 which faces away from the clutchdisc 4. The blind bores 11 are not formed in radially outwardlyextending projections of the pressure plate 1 but rather in that(annular) portion of the pressure plate which is provided with thefriction surface 10 serving to engage the clutch disc 4 when the clutchis engaged. The width of the surface 10 is indicated at 9; the blindbores 11 can be disposed substantially or exactly midway between theouter and inner annular surfaces of the pressure plate 1.

Each leaf spring 5 can be assembled of two or more discrete leaf springswhich accurately overlap each other and have registering openings 5c forparts of the respective first portions 12a of the connecting elements12. That surface or side of the illustrated leaf spring 5 which facesaway from the surface 10a of the pressure plate 1 is denoted by thecharacter 5d.

Each fully inserted connecting element 12 resembles a rivet blank withan end portion or head 14 at one of its axial ends, and such head or endportion of the connecting element overlies the surface 5d in the regionof the respective opening 5c to prevent the end portion 5b from movingaway from the surface 10a of the pressure plate 1 when the connectingelement 12 is properly anchored in the respective blind bore 11. Thefirst portion 12a of the connecting element 12 has a socket 17 which canconstitute a through bore or a bore which is closed at the end remotefrom the annular end portion or collar 14. The spreading element 13 isfully received in the socket 17 so that its outer end face is flush withthe outer end face 8 of the end portion 14 when the fastening device 7which is shown in FIGS. 1, 2 and 3 is fully installed. The element 13prevents any stray movements of the end portion 5b with reference to thepressure plate 1.

The end portion 14 of the illustrated connecting element 12 is integralwith the first portion 12a; however, it is also possible to make the endportion 14 integral with the spreading element 13 so that the endportion 5b of the leaf spring 5 is held against movement away from thesurface 10a of the pressure plate 1 when the spreading element 13 isdriven home to thereby effect requisite radial expansion of theplastically deformable (ductile) material of the first portion 12a ofthe connecting element 12. Radial expansion of the portion 12a ispreferably carried out in such a way that the portion 12a alsocompletely fills the opening 5c in the end portion 5b of the leaf spring5. The outline of the opening 5c preferably deviates from a circularoutline, i.e., such opening can have an oval or polygonal outline and isfilled with the material of the portion 12a when the installation of thefastening device 7 is completed. The material of the connecting element12 can be any metal or alloy which is capable of undergoing requisiteradial expansion in response to penetration of the much less deformablespreading element 13 into the axial socket 17 to thus ensure that theradially expand part of the portion 12a is held in pronounced frictionalengagement with the internal surface bounding the blind bore 11 of thepressure plate 1 and preferably also that the radially expanded part ofthe portion 12a completely fills the opening 5c of the respective endportion 5b of the leaf spring 5.

As can be seen in FIG. 3, the internal surface of the pressure plate 1in the blind bore 11 is provided with threads 16 which extend along aportion (15) of the axial length or depth of the blind bore. The threads16 can be replaced with another suitable uneven profile which ensures amore reliable retention of the portion 12a in the bore 11 in response toradial expansion of the portion 12a, i.e., in response to penetration ofthe spreading element 13 into the socket 17. The thread 16 is preferablyimmediately adjacent to the surface 10a and may but need not extend allthe way to the deepmost portion 11a of the blind bore 11.

It is clear that a similar or analogous result can be achieved if thethread 16 is provided on the external surface of the portion 12a of theconnecting element 12 and the internal surface of the pressure plate 1(in the blind bore 11) is merely provided with a profile whichapproximates or resembles the profile of the externally threaded regionof the portion 12a. Still further, it is possible to provide internalthreads 16 in the blind bore 11 of the pressure plate 1, to providesimilar or somewhat similar external threads on the external surface ofthe portion 12a, and to deform the external threads of the portion 12ainto exact mesh with the internal threads 16 of the pressure plate 1when the portion 12a undergoes radial expansion in response tointroduction of the spreading element 13 into the socket 17. All thatcounts is to ensure that the frictional engagement between the externalsurface of the portion 12a and the surface bounding the blind bore 11will suffice to reliably prevent uncontrolled extraction of theconnecting element 12 from the bore 11 and opening 5c.

Prior to penetration of the spreading element 13 into the interior ofthe connecting element 12, the socket 17 preferably includes asmaller-diameter inner portion 17b and a larger-diameter outer portion17a. The preferably frustoconical front end portion or leading end 13aof the spreading element 13 is introduced into the larger-diameterportion 17a and the element 13 is thereupon forcibly introduced into thesmaller-diameter portion 17b of the socket 17 to thus expand the portion12a of the connecting element 12 in the aforedescribed manner. The apexangle of the conical portion 13a is preferably between 30 and 60degrees, most preferably approximately 40 degrees. This has been foundto facilitate penetration of the spreading element 13 into the portion12a of the connecting element 12. As further shown in FIG. 3, thetrailing or upper portion 13b of the spreading element 13 is preferablya mirror image of the leading portion 13a so that one need not becareful in selecting that end portion of the element 13 which is to beintroduced into the larger-diameter portion 17a of the socket 17preparatory to spreading of the portion 12a into intimate contact withthe surface surrounding the blind bore 11. Another advantage of thefrustoconical rear end portion 13b of the spreading element 13 is thatit can be completely and closely surrounded by the material of the endportion 14 (note FIG. 1) when the spreading element 13 is driven home sothat its upper end face (as viewed in FIG. 3) lies flush with theexposed side or surface 8 of the end portion 14 of the connectingelement 12. This ensures that the spreading element 13 is not likely tomigrate axially of the connecting element 12 and to possibly weaken theconnection between the portion 12a and the surrounding material of thepressure plate 1.

The device which is used to drive the spreading element 13 into thesocket 17 of the connecting element 12 is not specifically shown in thedrawing. Such device causes the element 13 to enter the smaller-diameterportion 17b of the socket 17 and to expand the portion 12a so that itfills the thread 16 in the internal surface of the pressure plate 1 withattendant permanent anchoring of the connecting element 12 in the blindbore 11. Also, the device which drives the spreading element 13 home canbe used to ensure that the exposed end face of the fully introduced(i.e., fully confined) spreading element 13 is flush with the exposedend face 8 of the end portion 14 as well as that the end portion 14adequately surrounds the trailing end portion 13b of the fully insertedspreading element.

FIG. 4 shows a slightly modified spreading or expanding element 18having a substantially spherical (preferably hemispherical) leading endportion 18a corresponding to the frustoconical end portion 13a of thespreading element 13. The rear end portion 18b of the spreading element18 can resemble the front end portion 18a and can serve the same purposeas the rear end portion 13b of the spreading element 13, i.e., it can beclosely surrounded by the material of the end portion 14 when thespreading element 18 is driven home in lieu of the spreading element 13.

It is further clear that other types of spreading elements can be usedwith similar or equal advantage. For example, the central portion of thespreading element 13 or 18 need not constitute a cylindrical pin orpost, i.e., such central portion can have a polygonal outline withoutdeparting from the spirit of the invention. Also, one end portion of thespreading element can have a conical (preferably frustoconical) outlineand the other end portion of the same spreading element can have another(e.g., spherical and preferably semispherical) outline. Furthermore, thecross-sectional area of the central portion of the spreading elementneed not be constant all the way between the end portions 13a, 13b or18a, 18b; for example, the cross-sectional area of the central portioncan increase in a direction from the leading portion 13a or 18a towardthe rear end portion 13b or 18b, especially if the rear end portion isclosely surrounded by the material of the end portion 14 so that thefully embedded spreading element is prevented from leaving the socket 17of the connecting element 12.

An important advantage of the improved fastening device is that theconnection between each leaf spring and the pressure plate 1 is not onlyhighly reliable but also compact and extremely unlikely to permit straymovements of the end portions 5b of leaf springs 5 and/or completedetachment of such leaf springs from the pressure plate. It has beenfound that radial expansion of the first portion 12a of the connectingelement 12 invariably ensures the establishment of a frictional and/orform-locking engagement with the pressure plate which can guaranteereliable and permanent connection between the leaf spring and thepressure plate under all foreseable circumstances of use of the frictionclutch.

Another important advantage of the improved fastening device is that itensures uniform distribution of forces along the entire or nearly entireinternal surface surrounding the blind bore 11 and along the entire ornearly entire external surface of the portion 12a of the connectingelement 12 so that certain portions of the connecting element are highlyunlikely to be subjected to pronounced or excessive localized stresses.Also, any appreciable play between the end portion 5b of the leaf spring5 and the adjacent portion of the pressure plate 1 is practicallyimpossible. This contributes to longer useful life of the fasteningdevice and to more predictable operation of the friction clutch.

While it often suffices if the blind bore 11 is simply surrounded by amore or less cylindrical internal surface of the pressure plate 1, theprovision of aforediscussed unevennesses in the form of threads 16 orthe like (at least along a certain portion (15) of the internal surfaceof the pressure plate) can contribute significantly to greaterreliability and safety of the fastening device. As mentioned above, thethreads 16 or other types of unevennesses need not extend along the fullaxial length of the blind bore 11 but can be provided only in a selectedportion or in certain isolated (spaced apart) portions of such internalsurface. The provision of unevennesses at the internal surface of theblind bore 11 (and hence at the external surface of the radiallyexpanded plastically deformed portion 12a) not only increases the safetyof the fastening device but also increase the area of surface-to-surfacecontact between the portion 12a and the pressure plate 1 with attendantreduction of stresses per unit area of such surfaces and an even morepronounced reduction of the likelihood of damage to the fastening devicein response to the application of pronounced stresses tending to extractthe portion 12a from the blind bore 11.

The permanently installed spreading element 13 or 18 also contributes toreliability, longer useful life and safety of the improved fasteningdevice. As mentioned above, the spreading element 13 or 18 is introducedfirst into the larger-diameter portion 17a of the respective socket 17and is thereupon forced into the smaller-diameter portion 17b withattendant radial expansion of the portion 12a and resulting reliableengagement between the external surface of the portion 12a and theinternal surface of the adjacent portion of the pressure plate 1. Theprovision of the aforediscussed tapering leading end portion 13a or 18afacilitates introduction of the respective spreading element 13 or 18into the socket 17 of the selected connecting element 12 and furtherensures predictable and gradual radial expansion of the portion 12a intorequisite frictional and/or form-locking engagement with the pressureplate 1.

If the annular end portion 14 of the connecting element 12 is alreadypresent before the portion 12a is introduced into the blind bore 11, theend portion 14 can serve as a means for determining the extent ofpenetration of the portion 12a into the bore of the pressure plate 1.However, it is equally within the purview of the invention to form theenlarged end portion 14 subsequent to introduction of the portion 12ainto the blind bore 11, e.g., by resorting to a tool which drives thespreading element 13 or 18 into the socket 17 and, when the introductionof the spreading element is completed, converts the outer end of theportion 12a into a collar 14 which resembles the head of a rivet, whichholds the end portion 5b of the respective leaf spring 5 againstmovement away from the surface 10a of the pressure plate 1, and whichpreferably surrounds the rear end portion 13b or 18b of the fullyintroduced spreading element 13 or 18 to thus prevent axial movement ofthe spreading element out of the socket 17. Conversion of the outer endportion of the connecting element 12 into a ring 14 or the like canresult in some radial expansion of the adjacent part of the tubularportion 12a so that the latter completely fills the opening 5c in theend portion 5b of the leaf spring 5. This ensures predictable andoptimum transmission of forces between the leaf spring 5 and thefastening device. It is clear that the opening 5c can be filled with thematerial of the tubular portion 12a during introduction of the spreadingelement 13 or 18, i.e., additional tendency to expand the portion 12awithin the confines of the opening 5c during the formation of the endportion 14 then merely constitutes a safety measure to invariably ensurethat such opening is filled with the plastically deformable material ofthe connecting element 12 when the making of the fastening device iscompleted.

The provision of openings 5c whose outline deviates from a circularoutline is often desirable and advantageous because this greatly reducesthe likelihood of turning of the end portions 5b about the tubularportions 12a of the respective connecting elements 12 in the fullyassembled fastening devices. When a non-circular opening 5c is filledwith the plastically deformable material of the portion 12a, therespective end portion 5b is reliably held against any stray movementsrelative to the pressure plate 1 and/or the respective fastening device.

FIG. 5 illustrates a modified fastening device 7' which includes asingle part, namely, a connecting element 21 having an axially extendingsocket 20 in its elongated first portion 21a and a collar-like endportion 14 which overlies the upper side 5d of the leaf spring 5. Thesurface bounding the blind bore 11 is formed with internal threads 16and/or such threads are provided on the external surface of the portion21a. The fastening element 7' does not comprise a permanently installedspreading element; the means for expanding the portion 21a is aspreading tool 19a provided at the lower end of a handle 19 and taperingin a direction away from the handle. The tip 19b of the tool 19a canconstitute or resemble the frustum of a cone. When the radial expansionof the plastically deformable material of the element 21 in the bore 11and in the opening of the leaf spring 5 is completed, the tool 19a isextracted so that the socket 20 remains open. The shoulder 19c of thehandle 19 can serve as a means for flattening or smoothing the exposedside of the end portion 14 and for ensuring that this end portion liesagainst the side 5d of the leaf spring 5. The shoulder 19c can be saidto constitute a means which converts the end portion 14 into a structureresembling the head of a rivet and which thereby ensures that the leafspring 5 invariably contacts the adjacent surface of the pressure plate1 when the installation of the fastening device 7' in the blind bore 11and in the opening of the leaf spring is completed. As explained above,such conversion of the end portion 14 into a structure resembling thehead of a rivet can take place simultaneously with radial expansion ofthe portion 21a into frictional and/or form-locking engagement with thematerial of the pressure plate 1 or simultaneously with permanentintroduction of the spreading element 13 or 18 into the socket 17 of aconnecting element 12. However, it is also within the purview of theinvention to introduce the spreading element 13 or 18 or to introduceand then extract the tool 19a in a first step, and to thereupon treatthe end portion 14 of the connecting element 12 or 21 in a separatesecond step. Such deformation of the end portion 14 invariably ensuresthat the opening of the leaf spring is filled with the material of theconnecting element 12 or 21 if the opening is not filled duringintroduction of the spreading element 13 or 18 or during introduction ofthe extractible spreading tool 19a.

Without further analysis, the foregoing will so fully reveal the gist ofthe present invention that others can, by applying current knowledge,readily adapt it for various applications without omitting featuresthat, from the standpoint or prior art, fairly constitute essentialcharacteristics of the generic and specific aspects of my contributionto the art and, therefore, such adaptations should and are intended tobe comprehended within the meaning and range of equivalence of theappended claims.

I claim:
 1. A method of establishing a torque transmitting connectionbetween substantially coaxial rotary first and second components in afriction clutch wherein one of the components is movable axially of theother of the components and the transmission of torque takes place byway of at least one coupling member, comprising the steps of affixing afirst portion of the coupling member to the first component; providing asurface of the second component with a blind bore; forming a secondportion of the coupling member with an opening and placing the secondportion into a position of overlap with the surface of the secondcomponent so that the opening registers with the blind bore while a sideof the second portion of the coupling member faces away from the surfaceof the second component; and fastening the second portion of thecoupling member to the second component by means of a metallicconnecting element, including passing the connecting element through theopening so that a first portion of the connecting element is received inthe blind bore and an end portion of the connecting element extendsbeyond the side of the coupling member, at least partially expanding thefirst portion of the connecting element radially of the blind bore sothat the first portion of the connecting element is anchored in thesecond component, and causing the end portion of the connecting elementto overlie the side of the second portion of the coupling member in theregion of the opening to thereby hold the second portion of the couplingmember against movement away from the surface of the second component.2. The method of claim 1, wherein the one component is the pressureplate and the other component is the housing of the friction clutch, thecoupling member comprising at least one leaf spring and furthercomprising the steps of imparting to the first portion of the connectingelement a tubular shape and providing the connecting element with asocket which is open in the region of the end portion of the connectingelement, said expanding step including driving into the socket aspreading element so as to maintain the first portion of the connectingelement in expanded condition.
 3. The method of claim 2, wherein thefirst portion of the connecting element is integral with the endportion, said step of providing the connecting element with a socketincluding forming the socket with a smaller-diameter portion for thespreading element and with a larger-diameter portion.
 4. The method ofclaim 2, wherein the first portion of the connecting element consists atleast in part of a plastically deformable material which surrounds thespreading element in the socket, said driving step including expandingthe socket so as to urge the plastically deformable material against andto cause such deformable material to conform to the surface surroundingthe corresponding portion of the blind bore.
 5. The method of claim 1,wherein the one component is the pressure plate and the other componentis the housing of the friction clutch, the coupling member comprising atleast one leaf spring and further comprising the steps of imparting tothe first portion of the connecting element a tubular shape andproviding the connecting element with a socket which is open in theregion of the end portion of the connecting element, said expanding stepincluding introducing into the socket a spreading element so that anouter end portion of the spreading element is disposed at the open endof the socket and is closely surrounded by the end portion of theconnecting element and that a second portion of the spreading elementwith a cross-sectional area greater than that of the outer end portionis received in the socket witin the confines of the opening and theblind bore.
 6. A method of establishing a torque transmitting connectionbetween substantially coaxial first and second rotary components of afriction clutch wherein the first component includes a pressure platewhich is movable axially of the second component and is biased axially,comprising the steps of securing a first portion of each of a pluralityof leaf springs to the second component so that a second portion of eachleaf spring overlies the pressure plate and a side of each secondportion faces away from the pressure plate; providing the second portionof each leaf spring with an opening; and fastening each second portionto the pressure plate by a discrete connecting element, includinganchoring a tubular portion of each connecting element in the pressureplate so that each tubular portion extends through the opening in thesecond portion of the respective leaf spring, causing an end portion ofeach connecting element to overlie the side of the second portion of therespective leaf spring, and providing each connecting element with asocket extending inwardly from the respective end portion.
 7. The methodof claim 6, wherein the second portions of the leaf springs overlie anexternal surface of the pressure plate and further comprising the stepof providing the external surface of the pressure plate with blind boreseach in register with the opening in the second portion of a leaf springand each bounded by a profiled internal surface of the pressure plate,said anchoring step including anchoring the tubular portions of theconnecting elements in the respective blind bores.
 8. The method ofclaim 6, further comprising the steps of making the first portions ofthe connecting elements at least in part of a plastically deformablemetallic material so that the first portions of the connecting elementscan be readily expanded in the course of said anchoring step to bepressed against and to conform to the surfaces surrounding thecorresponding portions of the respective blind bores.